Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
Example 28−1. Finding the process associated with a PID
#!/bin/bash
# pid−identifier.sh: Gives complete path name to process associated with pid.
ARGNO=1 # Number of arguments the script expects.
E_WRONGARGS=65
E_BADPID=66
E_NOSUCHPROCESS=67
E_NOPERMISSION=68
PROCFILE=exe
if [ $# −ne $ARGNO ]
then
echo "Usage: `basename $0` PID−number" >&2 # Error message >stderr.
exit $E_WRONGARGS
fi
pidno=$( ps ax | grep $1 | awk '{ print $1 }' | grep $1 )
# Checks for pid in "ps" listing, field #1.
# Then makes sure it is the actual process, not the process invoked by this script.
# The last "grep $1" filters out this possibility.
if [ −z "$pidno" ] # If, after all the filtering, the result is a zero−length string,
then
# no running process corresponds to the pid given.
echo "No such process running."
exit $E_NOSUCHPROCESS
fi
# Alternatively:
# if ! ps $1 > /dev/null 2>&1
# then # no running process corresponds to the pid given.
# echo "No such process running."
# exit $E_NOSUCHPROCESS
# fi
# To simplify the entire process, use "pidof".
if [ ! −r "/proc/$1/$PROCFILE" ] # Check for read permission.
then
echo "Process $1 running, but..."
echo "Can't get read permission on /proc/$1/$PROCFILE."
exit $E_NOPERMISSION # Ordinary user can't access some files in /proc.
fi
# The last two tests may be replaced by:
# if ! kill −0 $1 > /dev/null 2>&1 # '0' is not a signal, but
# this will test whether it is possible
# to send a signal to the process.
# then echo "PID doesn't exist or you're not its owner" >&2
# exit $E_BADPID
# fi
exe_file=$( ls −l /proc/$1 | grep "exe" | awk '{ print $11 }' )
# Or exe_file=$( ls −l /proc/$1/exe | awk '{print $11}' )
#
# /proc/pid−number/exe is a symbolic link
# to the complete path name of the invoking process.
if [ −e "$exe_file" ] # If /proc/pid−number/exe exists...
Chapter 28. /dev and /proc 313